The present invention relates to a composite material and method of its manufacture, wherein the composite material has improved acoustical and surface hardness properties for use as an acoustical panel.
The manufacture of wet-laid acoustical panels typically includes a wet process having separate dilute water streams of fiber, fillers and binder which are mixed together to create a slurry. The fibers are either organic or inorganic. Usually the fibers are inorganic for fire resistance. A typical binder is starch. Fillers may include newsprint (which also acts as a binder), clay, and perlite. A typical panel wet-forming process involves the successive steps of depositing a wet slurry onto a conveyor screen, draining water from the slurry through the screen. The process also includes suctioning for further water removal, press rolling for compressing out additional water and finally hot air drying the slurry as it is cast on the screen. Upon entering a drier, the wet panel typically has 60-70% water content.
One of the most important aspects of a ceiling board is its sound absorption function. Artisans have employed many different techniques to increase sound absorption of acoustic panels, including apertures, fissuring, and striating. The relative noise reduction capability is expressed in terms of a noise reduction coefficient (NRC). Historically, wet processed acoustical panels have not had a very high NRC when compared to dry processed ceiling boards, such as those made from fiberglass batts. However, there are many disadvantages associated with the use of fiberglass. Disadvantages include the cost of the fiberglass relative to natural fibers, complexity and costs associated with manufacturing fiberglass acoustical panels with organic binders, health and environmental concerns associated with the use of organic solvents and organic binders in the manufacture of fiberglass acoustic panels, and the lack of strength associated with acoustic panels having inner cores comprised of fiberglass batts.
In the manufacture of wet-process acoustical panels, sound absorbent composite materials should achieve an acceptable level of sound absorbency. This is usually done by reducing the density of the panel or increasing panel thickness. Competing with the requirement of high acoustical absorbency is the need for a relatively stiff material to provide sufficient structural integrity and sufficient surface hardness to resist punctures and dents which may occur during the manufacture, transport, installation or use of the product. Additionally, a minimum thickness is also desirable to lower the material cost associated with the manufacture of acoustical panels from the acoustically absorbent material.
Unfortunately, wet-process materials that exhibit sufficient stiffness and surface hardness are usually quite dense, have small and closed cells, and do not display acceptable sound absorption characteristics. Furthermore, wet-process materials with highly acoustical absorbent properties are much less dense due to increased porosity, and therefore do not exhibit sufficient stiffness and surface hardness properties required for acoustic panel applications. Additionally, since traditional wet-processing techniques require a vacuum drawn through a cross-section of the wet-laid material to remove water, a significant porosity size gradient arises through a cross-section of the panel, which further degrades the acoustic attenuation properties and strength of the finished panel.
Frequently, artisans will increase the relative amount of fibers within a composition to increase material porosity and sound absorbency of the material. However, formulations that contain high amounts of natural fibers such as cellulose in combination with high amounts of perlite normally cannot achieve a uniform distribution of large open-celled voids, because the cellulosic fibers collapse onto each other during the vacuum drying process. In addition, the vacuum process tends to order the fibers into a two-dimensional configuration parallel with a plane upon which the wet-laid material lies, which decreases multi-dimensional stiffness of the finished product. Finally, the perlite tends to separate from the fibers and float to the surface of the aqueous solution during the panel forming stage, further weakening the final product.
For example, U.S. Pat. No. 5,277,762 discloses a material and process of manufacturing which overcomes the problem of fiber collapse and perlite separation by floating the slurry prior to draining the water. The floating process allows the use of high levels of cellulose and perlite, but at a relatively low density to maintain the necessary high porosity. Although this process achieves a low-density material with desirable acoustical properties, the process produces boards having low surface hardness and stiffness.
Other references illustrate the achievement of structural integrity at the cost of lowering acoustical absorbency of the material. For example, U.S. Pat. No. 5,395,438 discloses an acoustical tile composition having no wool content and high levels of expanded perlite or mineral fillers with a starch gel binder to aid in mold forming of a structurally sound acoustic panel. Although the resulting acoustic panel displays acceptable hardness, the panel does not exhibit the noise reduction characteristics needed for an acoustical panel application due to the density of the panel.
Others have attempted to manufacture acoustic panels by utilizing a foaming process to achieve sufficient sound absorbency. For example, U.S. Pat. No. 3,444,956 discloses a latex, pigmented, foam-surfaced acoustical body. This overlay structure, although providing acoustical transparency to the baseboard, does not exhibit sufficient hardness for an acoustical panel application and is therefore not desirable.
Therefore, there is a need to create a modified wet-process for manufacturing a novel acoustical panel having a high acoustic absorbency, but with sufficient structural integrity and surface hardness to serve as an acoustical panel for use in ceilings and walls.
The present invention provides for an acoustical panel formed from a fibrous, open-celled material comprising up to about 50% by weight fibers, between about 3% and about 10% by weight binder, between about 20% and about 75% by weight filler and about 0.01% to about 2.0% by weight surfactant. Additionally, voids are formed within the panel having an average distribution size diameter of about 50 xcexcm to about 250 xcexcm. The voids are distributed evenly throughout the panel with very little striation.
Furthermore, an acoustical panel comprising a dried open-celled material formed from an aerated foamed slurry is described. The aerated foamed slurry comprises on a wet percent weight basis up to about 30% by weight fibers, up to 6% by weight binder; about 3% to about 45% of a filler, about 40% to 70% by weight water and about 0.003% to about 1.2% by weight surfactant. The dried open celled material also has a dry density between about 10 lb/ft3 and about 18 lb/ft3 and a NRC factor of at least about 0.65.
A method of producing an acoustic panel comprises the steps of preparing a dry mixture of fibers, binder and filler and then conveying the dry mixture to a mixer. The method then mixes the dry mixture within the mixture to ensure proper distribution of the fiber, binder and filler. Next the dry mixture is combined with a water and surfactant to form a slurry. The slurry is then aerated to form a foamed slurry that is then dried. Voids are created as the foamed slurry dries. The voids have an average distribution size diameter of about 50xcexcm to about 250 xcexcm.
Fibers suitable for use with the present invention may include, but are not limited to, organic fibers such as cellulosic fibers derived from wood or paper products. Additionally, the composition may also utilize inorganic fibers such as, but not limited to, fiberglass, metal slag wool, rock wool or mineral wool. Furthermore, examples of fillers may include, but are not limited to, clay, perlite, limestone, diatomaceous earth, talc, silicates or wollastonite. Additionally, the composition may include any typical binding material for acoustic paneling material including, but not limited to, cornstarch, modified starches, polyvinyl acetates, polystyrene acrylics, polystyrene butadiene.
The material comprising the acoustic panel derived from the ingredients mentioned above exhibits good acoustic and structural characteristics due to the process for manufacturing the material. The process comprises the step of dry blending the fibers, filler and binder until the fibers are well dispersed through out the dry mixture. A conveying device feeds the dry mix to a high-intensity mixer. Simultaneously, the water and surfactant are added to the dry mix. The mixing process sufficiently agitates the wet and dry mixtures to create a foamed slurry by incorporating air into the mixture. The mixer drives the aerated, foamed slurry down to a bottom portion of the mixer, into a pump and finally through an extrusion die. The extrusion die includes an elongated orifice for extruding a sheet of the foamed slurry onto a conveyor for drying. The extruded sheet is dried by conventional means and is then suitable for use as an acoustic panel.
In an alternative embodiment of the present invention, surfactant may be added as a foamed liquid for further facilitating the creation of a foamed slurry. The liquid, which would generally comprise water and surfactant, may be agitated to create a foam prior to its addition to the dry mixture. In still another embodiment, each material within the composition may be added via separate streams into the high-intensity mixer to create the foamed material.
Advantages of the present composition and process include full three-dimensional orientation of the fibers within the materials to ensure enhanced material strength and surface hardness. The relative range of void sizes within the slurry is narrow since a vacuum is not drawn through the slurry. Additionally, virtually no gradient in void size through the panel cross-section can be seen. The narrow void size range and the virtual elimination of a void size gradient across a cross-sectional thickness of the panel enhances the acoustic absorbency of the panel while increasing its mechanical strength.